Hydrogen containing gas mixtures can be obtained by the incomplete combustion of biomass. Devices which support this operation are typically referred to as gasifiers. During World War II, a large number of small gasifiers were fabricated and installed on vehicles to provide a combustible gas stream to power the vehicle's internal combustion engine from biomass because gasoline was difficult to obtain. Today's emphasis on long term sustainability, including reducing carbon footprint and the increasing cost of fossil oil, is renewing interest in these gasifier-engine systems.
A typical small gasifier-engine combination operates by drawing air through the gasifier via the partial vacuum created in the engine's intake manifold. A range of parameters can be adjusted to supply a wide range of gasses to the engine. The gas stream will typically include nitrogen, carbon monoxide, hydrogen, carbon dioxide, and water vapor. The carbon monoxide and hydrogen are combustible, while the other gasses are diluents which generally reduce engine performance. Operating the gasifier with a high temperature in its char reducing region and supplying it with sufficient water will result in relatively high hydrogen concentrations, with very little water or carbon dioxide. For example, a gas stream including 30% nitrogen, 30% carbon monoxide and 30% hydrogen is possible.
Hydrogen has a wide variety of commercial uses beyond running the local engine. As such, it may be desirable to divert some of this hydrogen in concentrated form for other processes such as: (i) to hydrogenate biomass to liquid fuels, (ii) to make ammonia as a precursor to fertilizers, (iii) to provide a safe cooking and heating fuel for the developing world, and (iv) to power fuel cell and hydrogen compatible engines (the classic hydrogen economy).